The present invention relates to high gradient magnetic separation (HGMS) devices, and in particular, to an improved HGMS device useful for the isolation of biological entities.
Numerous magnetic separation techniques have been developed over the years in connection with efforts to improve mineral processing. More recently, magnetic separation techniques have been used effectively for locating and isolating biological entities, such as cells, proteins, organelles, enzymes, and the like. These techniques typically involve introducing magnetic particles into a liquid sample containing a mixture of the biological entity to be isolated with various other biological entities. In most instances, the magnetic particles are coated with a material having an affinity for the target biological entity thus causing the magnetic particles to become attached to the target biological entity in preference to the other entities admixed therewith. Subsequently, a magnetic field provided by an electromagnet, for example, is applied to the liquid sample, thereby immobilizing the magnetic particles carrying the target biological entities against the walls of the sample container. The target biological entities are then separated from the liquid sample. For specific applications of such techniques, see: Giaver, U.S. Pat. No. 4,018,886; P. Dunnill et al, 16 Biotechnology and Bioengineering 987 (1974); R. Molday et al, 268 Nature 437 (1977); and P. Kronick et al, 200 Science 1074 (1978).
For certain applications these techniques have not been completely satisfactory because the population of biological entities retained by the magnet also contains other undesired substances as well. Removal of the undesired substances often requires repeated passing of the mixture through the separation device.
Advances in the art of magnetic separation have led to the development of HGMS devices in which it is possible to separate very weakly magnetic materials of small particle size. These devices are well known to those skilled in the art, and typically comprise a separation vessel, e.g., a canister, containing a ferromagnetic material, such as steel wool, through which the materials to be separated are passed. High field gradients result from applying a relatively uniform background magnetic field to the ferromagnetic filamentary material. The strong magnetic forces produced by the high field gradients at the edges of the filaments are effective in immobilizing particles of even weakly magnetic material.
Although HGMS devices of the type described above have been employed with varying degrees of success in chemical processing, pollution control, and the beneficiation of non-ferrous low grade ores, such devices have not produced completely satisfactory results when applied to the separation of biological entities. The reason is that both the biological entities sought to be isolated and other undesired entities often adhere to the metal filaments even after the applied magnetic field is reduced to zero. In certain instances, contact between the metal filaments and the biological entities has actually damaged the latter.